Telephone-exchange system



E. H. cLAlK .ELEPHONE XCHANGE SYSTEM May 29, 1923.

Filed May 19, 1920 5 Sheets-Sheet 1 May 29, 1923. M5653? E. H. CLARK TELEPHONE EXCHANGE SYSTEM Filed May 19. 1920 5` sheets-sheet 2 May 29, E923."

E.A Hl CLARK TELEPHONE EXCHANGE SYSTEM l Filed may 19. 1920 trail dgn/k H. by Ag 5 Sheets-Sheet 3 /H van for:

[Va/k.

May 2Q, B923. 11,456,537 E. H. CLARK l TizmazPHoNf: EXCHANGE SYSTEM Filed May 19. 1920 5 sheets-sheet 4 I I l j N 09 o 00o o 0 o o 0 o u w no y on Go o oo c? oo o o0 oo o0 I D 0 D 0 O www.

May 29, E923.

E. H. -CLARK TELEPHONE EXCHANGE SYSTEM Filed May 19. 1920 5 Sheets-Sheet 5 Hwvmfas /M van for:

Patented May 29, lEZ. i

` ,ir rA rsitr-isrics.

EDGAR H. CLARK, OF RICHMOND HILL, NEW YORK, ASSIG'NOR CO WESTERN ELECTRIC COIiIPAlSTY,` INCORPORATED, OF NEW YORK, Y., A COlzuPOE/ATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed. May 19,

[o all fui/mm 'it may concern.'

Be it known thatv l, EDGAR H. CLARK, a. citizen ofn the United States, residing at. Richmond Hill, in the county of Queens, State'ot New York, have invented certain new and useful Improvements in Telephonelilxchange Systems, of which the following is a' full, clear,y concise, and eXact description. Y i

`This invention relates totelephone exchange ysystems .involving a plurality otk offices and particularly to systems in which inter-oflice connections are established in part by the use of machine switching apparatus.

The object of the invention is the provision, in telephone systemswhere operators are employed ormanually extending connections-over trunksleading' to succeeding switching 1 devices, of means for indicating to the operator the identity of yan automatically selectedv trunk tobe used by her in eX- tending such connections.

A feature of the invention relates to an arrangement; 'in systems of this character wherethe` trunks at an operators position are divided into groups, with progressively operable switching devices, one vfor each group, for automatically selecting an idle trunk from any group; in ywhich the extentot operation of a progressively operable indicator selecting mecha-nismjis determined by the particular switching device taken for use to indicate to the operator the designation of the group containing the selected trunk and also the location of the trunk insuch group. v

Another teature relates to the provision of a. plurality ottrunk selecting switches, one.l for. each group oftrunks, arranged to be serially operated 4to select a group containing an idle trunk and to selectv the idle trunk in such group.,A and indicator selecting switches arranged to be progressively `operated in laccordancewi'th the particular trunk selecting switch taken :toruse' and also in accordancewith theextent-,oiA operation of said particular switch for indicating to the op- 'erator the designation of the selected idle trunk. i I

Other featuresfcontemplated by the in# vention will become more apparentfrom a consideration of; the following description 'and appended claims. i

1920. Serial No. 382,502.

.Referring to the drawing vwhich constitutes a part oit the disclosure, lFigs. 1 to 5 inclusive, when arranged in the` order shown.

tion in a manual office provided with cordv circuits for extending subscribers lines over interoilicetrunk lines outgoing to distant mechanical offices. Fig. 2 and 3 show two oi a series of trunk selecting switches for.

automatically selecting an idle. trunk outgoing from the operators position to the desired mechanical oiiice. `Fig. 4 shows, on the right, a sender selector. switch for associatingan idle sending mechanism with the selected outgoing trunk, and` on the left, anvoperators position switch for associating the equipment at the calling opera-tors position with the selected outgoing trunk and `with the selected sending mechanism. F ig. fillustrates the controlling and indieating` equipment at the operators position.

ln the system disclosed, connections are established by the operators in a manual originating oiiice to any of a plurality of distant mechanical oilices. For each niechanical otlice to which the operators in the manual ohce have access, there is p rovided a group` otinterconnecting trunk lines terminating in machine switches at themechanical office. These groups ci. trunks are multipled so as to 'appear inv calling jacks at each of the manual operators positions. The operator responds, in the usual inanner, tothe initiation of a callfon a sub- Scribers line which terminates at her position. itscertaining the name olf the called oliice and the number of the wanted line in that oiiice, she 'manipulates the necessary a'ppai'atus at her position, which causes the automatic `selection of 'an idle trunk outgoing. to the called oliice, the lassociation of anidle sending mechanism with her position and the visual indication ot the designation ot the selected trunk. She then sets up the number of the called lineon a keyboard at her positi'onand completes the connection by` inserting the calling plug of her cord' circuit in the jack of .the selected outgoing trunk. The manipulation ot 4the'keylooard causes the desired designation to be registered on the sending mechanisniwhich thereupon serves to control, over the selected trunk, .the -operationqof lthe selective switches-in the called mechanical voffice.

A plurality of selecting units are assigned to each .group ofinteroflice,trunksleading to distant .mechanical offices, 4fone ofl which offices is represented at 120 in F ig. 1. One of these selecting units consists of a plurality of step-by-step trunk` selecting switches such as 200 and `800, afstep-by-step sender selecting switch 420, 4and a step-byystep loperators position switch 400. .Where the'ftraiiic between the ymanualofiice and the mechanical oiice 120 is comparatively heavy, Alarge `group of interoflice' trunks is necessary.- VI'n-a-smuch as the small stepby-s'tep--trunkselectingswitches 200 and 300 The sender selecting -switch 420 of fthe switching unit has access vto a plurality ofV fthe vsender selector 420Aand the series ofv only yhave va `capacity, of 20 trunks, it is necessary to provide `aVplur-a-lity of V'these switches for `the entire/group of outgoing trl'inks. Assuming thatthe outgoing trunk group` contains `160 trunks, eight trunk selecting switches are provided, each having access to a group of 20trunks, .with-means for successively .operating the .switches to select an'fidle trunk for use by the operator.'

sending mechanismsy common lto all-the operator's in the manual Oilice. The operators` selecting switch400, which, together with eight trunk selectors, 'comprises one selecting unit, l operates automatically in response to the initiation of a call lto select the op'erators position at which suoli call was initiated. allotterft10 is provided f' for the 'plurality of switching f units asf lott'ed switching unit individuall lto the vgroup of vtrunks leading Ato `such mechanical olice. yAny one of Ithe eight trunk selecting switches, such-as 200, 800, may be the first to be set Vin operation, dependent upon the group of 20 trunks finwhich an idle trunk was taken -foruse in the elast preceding connection. This switch hunts automatically7 and if no idle trunk -is found in its group off20, returns to normal position and initi-v y ates the hunting operation of the next succeeding :selecting switch in the series. The next switch hunts cver its group of .20 trunks and .so on runtl .fone Ioit fthe group :of

,duringvthe change-.over from one switchfto eight vswitches finds an idle trunk. A side switch ldesigua-ted yat2320iis provided for each -group'fof eight trunkselectingswitches and serves to control the operating circuits another.

In addition to the equipment thus i far described, the -operators vposition is also provided ywith a plurality ofnumber indicating lamps 'foridisplaying before the operator the hundreds, tens and units designations of the automatically selectedv outgoing trunk. Since -the trunk group fis said Vto contain 160 trunks, only-two-hundreds lamps, theNo. 0 andthe'No. 1 lampsareqrequired'.

A stepping switch *510 having ten'-positions is arranged -to select "the intens 'lamp' ideny tif-ying the number` of thefitens grou-p in either hundred 1in whichethelselected idle trunk is contained. A second stepping switch l520 isarranged to select one offten units lamps to indicate-the units -location cf the 4selected 1ktrunk in the group vofften.' 'As will be explained more fully hereinafter, these "lamp selecting switches are `set in -operation following the completion vvci 4-1-thetrunk .selecting operation vand are governed inthe extent of their motion by the posi'- tionin which the side switch 320lisstanding and lalso by `the position assumed Eby' the vparticular trunk 'selecting "switch inselecting the idle trunk." f" f "The operatorsl position is further pro`v l vvided with a single row yoften non-locking keys 515. lBy depressing -theiproper `colnbination-of these' keys, the designation .of

the called line is yregistered onfthe sending mechanism selected yby the lswitch vd20. "It is not considered necessary to -show -and describethe Vsending' mechanism since rthe lsame does not `specifically concern the subject met# ter of the present invention. Any vsending mechanism suitable for controlling pqwer driven ,switches of the revertive` impulsel type may/be employed.A A 'sender 'of ithe specific type shown rand described in detail I in `the British' patent to VVe'sternr Electric Company, Incorporated, No.v 173,009, ac cepted December 12, 1921mayjbe utilized in vthis system. Having given av general outline ofthe system, a detailed l'description of the operations involved in the establishment of a connection Will-now be ltaken up.

`Assume that lthe subscriber at substation' 100, Whose line terminates in the manual o'llice. wishes-to converse with lthe, subscriber substation' circuit, `rstunning Vf-t1l,-rouglri A:the

Contact and inner armature. cfuellayfld Il v f ruit.

the right-hand winding of relay 103 to ground. Relay 10.3 becomes energized and closes a circuit 4for the illumination of the calling line lainp..104., The operator, ob-

serving the calling signal 104 answers by inserting the plug 102 of anidle cord'cirruit `in thejack 101 l of the calling line.

through the supervisory lamp 106, resistance 115, sleeve .of plug102, ysleere'of jackl 101, windingof relay 105` to ground. Relay 105 4opens'the circuitl of the line relay 102, which, in turn, deenergizes. time .a circuit is closed .from battery, through the lower left-hand winding of repeating coil 109, winding of supervisory relay 107, ring of plug 102, ring of jack 101,. over the calling line circuit, tip of jack 101, tip of y. upper left-hand winding of repeatingcoil- 109to ground.- Relay-107 be plug 102,

comes energized and completes a circuit vfrom battery, through the contact and armature of relay 107, resistances 116 and 115 to,v

groundthrough the winding. of relay 105.

vlRelayf105 remains energized in this .circuit and supervisoryA lamp` 106, being shunted, is not illuminated. The operatordepresses her listening key 117, which .connects her telephone set 118 intalking relation with the calling line., She then communicates with the calling. subscriber and receives the name of the wanted oiiice and the numerical designation of the desired` line in that oilice. Having received this information ytheoperator releases her listening key 117 and depresses the o'flice lrey 500 at her positionl corresponding tothe name` of the called mechanical office 120.. f

In response to the depressione-f key 500 a circuitV is completed from battery, through the armatureA and'contact of relay 503, righthand windings of relays 502 and 501, vlefthand contact of'lrey 500 to 'ground at; the

right-handv armature and contactv of relayy 505. Relays 501 andv502are energized andl a holding circuit is established therefor independently of key 500. This circuit may bey traced from -battery,`through the armature and contact of relay503, left-hand windings of relays .502 and 501, vcontact 516,

attracted right-hand armature ofrelay 501, winding of relay 504, contact and Vinner righthand armature of relay'5-08 to ground;4

Relay 504 also becomes energized in this cir- The actuation of key` 500 closes another circuit traceable from battery`through the winding of relay 506', back contact and left-hand armature of relay 505,`right-hand Contact of key 500 torground. `Relay 506 en,-

ergizes and closes a circuit from battery, f

through relay 506 and relay 5051in series, contact and armatureof relay 506 to ground at-.the Contact and right-hand armature of relay 502` Relay 505, does not become en- .ergizechl however, until, keyz 500l is. released At the same to remove the shunt from around the winding thereof closed at the right-hand contact cuit is opened at the right-hand armature A circuit is thereupon completed from battery,

of relay 505.

The energization of relay 501 completes a starting circuit for initiating` the operation ofthe switches comprising the allotted switching unit. The starting circuit may be traced from` ground, through the left-hand.

closed contacts'of relay 504, outer left-hand armature and contact of relay 501, conductor 517, lower right-hand winding of balancing coil 415, winding of polarized relay 416, up-v per left-hand Winding of coil 415, to battery and ground. A parallel path leads through the lower windings of coil 415 to battery. Current flowing in this directionr through the windings of coil 415serves to imbalance the same whereby the polarized relay 416 attracts its armature. circuit is then closed from ground, contact and armature of relay 416, armature and contact of relay 413, brush 411 of allotter 410, through the left-hand winding of relay 408, individual to the allotted switching unit, right-hand winding of relay 409 to battery and ground. Relay 408 becomes energized and closes a locking circuit for itself from battery, through the right-hand Winding, contact and inner righthand.y armature of said relay to ground at the contact and upper armature of relay 428. Relay 409 also completes a holding circuit for itself from battery, through the lefthand winding and inner righthhand contacts and armature of said relay to ground at the contactand lower armature of relay 428.y Relay 408 establishes a circuit from battery, through the winding ofrelay 417, Contact and uppermost armature of relay 484, contact and innermost right-hand armature of relay 408, contact and upper armature of relay 428 to ground. Relay 417 closes a circuit from battery, through the winding of stepping magnetv407 of the operato-s'position selecting switch, armature and contact of said magnet, outer left-hand armature and conf tact of relay 417,. inding of relay 418, inner left-hand armature and contact of relay 417 to ground. Provided. the hunting brush 401. ofthe operators position switch -is standing on the terminal. representing a non-calling operators position,` relay 418 remains de energized by means of the following circuit closed directly to ground inv shunt of the winding of said rela-y: battery through the winding and armature and contact of magnet 407. outer left-hand armature and contact of relay 417, back Contact and armature of relay 418., hunting brush 401, conductor, 518, to yground at the contact 516 of relay 501 at the non-calling operators position.. Relay 418 therefore remains deenergized and high` resistance of relay 504.' The left-hand lthe 'stepping in agnet 40T interrupts its own circuitv and yadvances thebrushes 401 to L400 inclusive tofthefnext position terminals. The

positions, and finally reaches the't'erininals individual to the operato'i"s position atv which key5'00 was depressed.` Since relay 501,1at this position, is energizechvthe stepping cirJ cult. of magnet 407 1s no longer connected directly to 'ground at Contact `510 butnowf leads through the actuated contact '510 and4 attracted right-hand armature of relay 501 Y to the winding ot relay504fand thence to ground at the contact and `innerir1ght-hand windings ojl relays 502 and'501 areshunted vout at this point due to the application' Off` battery current at. the Contact 516 of relay 501. n These relays, however, remain enerf lgized in a Vcircuit completed ii'ro'in battery,

through the armature and contact of relay 503, right-'hand 'windings of vrelay V502v and 501inner left-hand armature andcontact of relay 501 to ground at the left-hand ar'rnarcomparatively high resistancey Olfrel ay `504 at the operators position, the'tlow of'c1rr1ent is suiliciently increased in thefci-rcuit above traced for causingthe energization oifnrelay 1418. Relay '418 therefore 5energfies in series withinagnet l407, but duetoits resistance,

said relay prevents the further operation of thestcppinpmagnet'. The 4brushes vot" the operat-ors position Aswitch are, thereforep brought to rest. The operation of relay4'f18' opens the circuit traced, 'orthe application o1 batterylcurient ythrough 1the'fwindinp;:ofI magnet 407l and thence to the contact 516 of y relay 501. Relay 418 furtherniore completes a circuit from battery` through" the armature" v. andcontact of relay 503,'left-hand Lwindings ofrelays 5,02 and 501', actuated contact 5116*, conductor 518, brush 401, armature and t'ront contact of relay 418, Winding vo-trelay i brushes 411 and 412 are ybr'fjuglit.'to' rest( 419 to ground. 'The resistance of relay 4129' is such that a suiiicien't amount 4of Acurrent is shunted away from theirinding otrelay 504 to permit this latter relay 'to release its armatures. Relays 502, 501, and 419 non'7 remain 'energized `in series With eachother. l Should" the hunting brush 401 of anotherswiitclhing unit, individual to the calledV mechanicalV ot'- lice, encounter the terminals individual 1to the ybusy* operators position, the stepping man# net 407 ofisuch other switching unit-Would continue to operate in a circuit *closed*v over the multiple terminals of the r-hunting brush 401, thro-ugh the armaturel and front contact of' relay418 and the Winding-of relay 419 ot' lthe switching unit shown. Relay 419 on' energizi'ng completes the following holding ein` f cuit 4for itself 'and Arelays! 502 and 5.01 inde. pendentlyaof*thelarniatureand front Contact 'otifelay i418 zgbattery, throughfthe armature and contactof `relay 503, leftihand windings oitfrelays 502and 501, Contact? 516, y'conductor 518, brush: 401, left-'hand Iarmature'and4 con-rv tact ioff'relay 408, Klett-hand armature and 1 contact and winding of relay 419 to ground.: RelayV 419, 'also-:establishes a circuitztrorn battery, through the Windin'gfof relay 482, contactand richtliandarmatureof relay 4119 to ground. ,r Y

L-Returning vnow to Vthe `.point `where relay 408 and consequently, 'relay 417 Ifof the a1- lotted switching unit 1:were lrstenergized@ description "will be-:given ,of they allotment of' the' next idle switching unit forfuse in con-- nection with asub'sequent call,- VWhen E'relay 417 is energized, a-circuit isl'established .from batteryg-:throughthe lowerlett-hand Winding ofco'il 1,415, Awinling of polarized :relay 416,

leads through 'the flipper windings p of o coil 415. Current flowing fin this `direction l 1 .through the ywindings lof coil 415 serves tol ture and contact of "relay 504. Due'to the lbalance 'the `sa1ne,-there`by causing the polar- 'izedre'lay y'416fto retract'its armaturei The energization of relay' 409, Which ytakes Jplace simultaneously;with ftheoperation ofrelay 408, causesa circuittolbe closed t'roin loaftfv tory, through theiv'rn'dlng fand 'Contact and armature of the "allotter `stelzi'p'ing inag'net 414, brush :412, Contact l and outermost left-A ,ownl `circuit and advances the"brushes 411 and '412 `into engagement' vwith fthe terminals individual to the next succeedings'tvitchingl uniftfin the ,Qroup. Iffthis next unit ils-"busy, the relay 409 thereofgis energized andra -circuit is closed vfor the,V 'continued operation voff' Amagnet414.' The a'llotter switchcontinues to step, thereijore,A until'the 'first idle 'sviiitfc'lr-` i v ing Yunit in' the, Vgroup 'is found, at which time the stepping circuit is opened land the During the operation of the stepping magi j net 414, the sloiv'togrelease relay' 4,13 is main-,k vtained energized.I v'This relay, at vits arma-y ture and contact lioltlsopenthe starting cir'`v cuit liereinbeiore traced, through the brush' Y' 411 and the windings @f i-eiays 40e and l40'9 se that if any operator imbalances" the `coil 415`by depressing an office key Correspond-y inir to key 500, during thetiine theallotter swi'tclijfis. searching` forl an ,idle :sy'vitching*A unit, the start circuit `will ynot be f completed.

operate, following 'the selection'of "an fidle,

switching unit the slow to release :relay 'circuit may be completed at the armature and Contact of the polarized relay 416, when the coil 415 is unbalanced by the key 500 at 'another 'calling operators position and the allotted switching unit taken for use.

Vhen lthe relay 409 becomes energized an operating circuit is closed for the stepping magnet 427 of the selecting switch 420. rhis circuit may be traced from battery,'through the winding and armature and Contact of magnet 427, back contact and right-hand armature of relay 430, contact and outer right-hand armature of relay 409 to the test brush 426. If the brush 426 is standing on a terminal individual toa busy sending mechanism, a ground will be present on such terminal and magnet 427 becomes energized. The magnet 427 interrupts its own circuit and causes the advance of the brushes 421 to 426 inclusive to the next succeeding position. The test brush 426 engages a grounded terminal for each succeeding busy sending mechanism and the switch continues to operate under the control of magnet 427.

During the operation of the sender selecting switch 420, a circuit is maintained as follows for the relay 430: battery, through the winding and armature and contact of magnet 427, winding of'relay 430, contact and inner right-hand armature of relay 409` contact and lower armature of relay 423 to ground.l Relay 430 remains deenergized, however, due to the shunt circuit closed diyrectly to ground at the terminals of busy sending mechanisms encountered at the test brush 426. lWhen brush 426 engages an ungrounded terminal, identifying an idle sending mechanism, the shunt is removed from around the relay 430'and this relay attracts its armatures. The resistance of relay 430 now being included in series with the stepping magnet 427, such magnet does not receive sufficient current to continue its operation and the brushes of the switch 420 are consequently brought to rest. When the test brush 426 encounters the terminal individual to an idle sending mechanism, a battery potential is supplied from such mechanism over the test brush 426 and thence through the outer left-hand `armature and contact of relay 409, right-hand armature and front contact of relay 430, winding of relay 431 to ground. The manner in which busy sending mechanisms furnish groundpotential, and idle mechanisms furnish battery potential at the terminals cooperating with thetest brush 426, is shown and described in detail in the British Patent No.vv 17 3,009, accepted December 12, 1921. Relay 431 attracts its armatures and providesa substitute hold. ing ground for relay 409 for a purpose to be hereinafter explained. Relay 430,"at the time of its ene'rgization, also establishes a circuit from ba.ttery,"through the winding of relay 434, inner left-hand armature and contact of relay 430, front contact and riOhthand armature of relay 432 to ground. e-

rlay 434 energizes in this circuit and attracts its armatures.

At the same time that relays 408 and 409 initiate the operation of the operators position switch 400 and the sender selecting switch 420, a circuit is alsocom'pleted for the operation of the trunk selecting switches. It will be assumed that each of the series of eight trunk selecting switches, 300, 200, and so forth, is in its normal position.` As shown in Figs. 2 and 3, the brushes of the trunk selecting switches when in their normal positions are standing on the No. 21 contacts. That is to say, the trunk selecting switches are each provided with twenty-two positions, the first twenty of which are assigned to the corresponding group of twenty trunks and the remaining two positions are used for change-over operations as will presently appear. When, therefore, the relay 409 first attracts its armatures, an operating circuit is completed as follows for the stepping magnet 307 of the first trunk selecting switch, 300, in the series: battery, through the winding of magnet 307, armature and contact of said magnet, first position terminal and brush 324 of side switch 320, conductor 334, contact and innermost left-hand armature of relay 409, conductor 335, back contact and inner left-hand armature of relay 308, brush 322 and its first position terminal, conductor 336, test brush 302 of trunk selector 300 and its No. 21 contact to ground. Magnet 307 is energized, interrupts its own circuit and advances the brushes 301, 302, 303, 304, 305 and 306 respectively into engagement with their No. 0 contacts, which represents the No. 0 or first trunk in the first group of twenty trunks outgoing from the manual office to the called mechanical office 120. If this first trunk is busy, they brush 302 finds a ground potential on the test terminal thereof and stepping magnet 307 again energizes to advance the selector brushes onto the next set of terminals representing the No. 1 trunk in the first group. During the operation of the trunk selecting switch in testing the condition of the outgoing trunks, a parallel circuit is maintained as follows through the winding of relay 308: battery, through the winding and armature and contact of magnet 307, brush 324, conductor 334, innermost armature and contact of relay 409, conductor 335, winding of relay 303, back contact and armature of relay 32S, conductor337, contact and outermost left-hand armatureof relay 409 to ground. Relay 308, however, being shunted out by the direct circuit to ground at test brush 302 does not operate as long busy trunks are encountered. Assume thatf the Iirst half ot the iir'st group ot twenty trunks,` namely trunksNo. to No, 9, are busy.` The brushes of the selecting switchi300 are, therefore, advanced to their c No. 10 position terminals', which represent the first: trunky in the second. halt ot the group twenty.v In this position, A'the'fbrush lf engages the grounded-*terminal 338 and a circuit. isl closedl from rbattery through. the

winding of magnet' 327, armature and contact ot said magnet',=hrush 321 and itsiirst position terminal` conductor 339, brush 301,

andV terminaliy 338 to ground, The magnet 327 energizes, interrupts its (m'n'circuitand advances the'bru'shes. 32l`q 323,v 324,

and l326 ot-the side switch totheii'z second position terminals; It" thev lirst. orA No. 0 trunk in the second halt' ot' the iirst group ot 'twenty trunks is busy, the-steppingmag-v net` 307 is energized as-betore, the only ditference being that, the operating circuit therefor now leads throughthefsecond position terminals` ot' side switch brushes 324 and322.

Assumingthat all ot; the second? group oftrunksappearing'in the switch 300 are busy, the brushes continue to advance until they reach their'No. 20 positionterminals. In this position a; circuits established as follows: battery, throughV the winding and armature'and cont-act of' steppingmagnet 307, brush 324,and: its second position terminal, conduct-M334, contact and inner letthand armature of relay. 409,- conductor335, back Contact' and. inner lett-,hand armature ofrelay 308, brush 322:' and its second' position terminal, conoluctory 336, brush 302 and` its No.1,20 position terminal 340, con- 'ductor 341, andk winding of relay 328 to cuit 'from groundy through its lett-handv armature and Contact; brush 323 audits second: position te1minal,.conductor 342, Winding of stepping magnet 307' tok battery and` ground. Stepping `magnets 307 and 327, are `therefore simultaneously. energized Magnet, 307 by attracting its armature, opens the` above traced circuitl tori relay y328. Relay 328, in turn, opens the energizing circuit'ot stepping magnet V327.. Magnet. 327 deenergizes and. causes the brushes of the side switch to be advanced to their third position terminals. It may be well to observe, at.` this spoint,... that. the..A stepping closes itsarmaturefand contactfollowing the deenergization of: relay 3-28-,thehrushes of@ selecting` switch i300-.have advanced; to

ltheir No.21 position terminals. Relay. 308,

therefore, does not, energize in series, with stepping` magnety 307. The first trunk selecting switch300 has now beenrestoredlto its normalposition andi an operating circuit is immediately. establishedftostart. the; hunting operation of the second. selectingy switch 200 which has access. to the second' group` ot' twenty outgoingv trunksi. This operating circuit mayI be traced from battery, 4through the winding and armature and contact of' magnet 207 ofthe switchl 2.00, conductor; 2.110, brush 324 and its third position terminal, conductory 334, contact.4 anch innermost letthand armature of relay. 409, conductor back contact and. inner lleft-hand armature ot relay 308, brush 322.*andfits thirdiposition terminal, conductor 211., test brush 202'and its No. 21positionterminalto ground.. A parallel. circuit. is c. also. established for relay 308 from battery, through` thel winding and armature and contact otmagaiet.2.0.7,. conductor 210, brush 324 and; thence, as`- described, to conductor, 335, windingofI relay 308, back contact andfarmature,v of relay` 328, conductor; 337, to groundfatthe, outermost, armature..andf'contact ofrelay. 409.

Relay 308,vr honffever, remainsjdeenergizediso long, as itswindingisfshunted oiithy` a direct circuit to yground at the ,brush 20.2"? andf` busy test-terminals. y. i'

Assume that theV No. 9. trunkinthe first half f ofy the second group of i twenty`r served by the selectingswitcli 20.0,.is1the` firstidle trunk. tov beencountered- Hencethe stepping magnet;y 207f continues to advance.,VV the brushes ,201, 202, 203 204, 205 xanaige'ce until they, reach .the .terminals .cor-respendi'ngto the idle trunk. Noground'being ypresentron thertest. terminal of: this.v trunk, thesliunt which. has, heretofore. been v.maintained around theV windingjot relay 308.,.'isnow-- removedand this relay. energizes. inse-ries-with v rthe.steppingmagnet 207. j Magnett207" ceases to operate by. reason of. the-.resistaneeo't' relay 308 includedin its circuit... Itiwillf thus beseenthat the idle trunk selectedfisLtheN.

9 trunkin the first ten trunks-fotithepsecond group oit-twenty. Theretore, the number ot this `trunk is 29and'since it belongs-.tothe firstv hundreds group, its complete designa- Cil tionis 029. It will also be observed that the side switch 320 has taken one step for each group of ten trunks hunted over and is consequently standing in its third position cor responding to the third group of ten trunks in which the selected trunk appears. Moreover, the brush 206 ofthe trunk selecting switch 200 is standing on its No. 9 position terminal 212, which corresponds to the units location of the selected trunkin the first group 'of ten trunks served by the switch 200. The side switch and the trunk select- I ing'switch in assuming these positions corresponding to the tens and units location of the selected trunk later perform certain functions, as will presently be described, in determining the visual indication of the designation to identify to the operator the vnumber lof the selected trunk.

When relay 308 becomes energized a circuit is closed from ground, through the front contact and inner left-hand armature of said relay, side switch brush 322 in its third position, conductor 211, test brush 202 and thence to the multiple terminals of the selected trunk in all other trunk selecting switches of the group of selecting unitszhaving access to trunks leading to the mechanical office 120. In this manner, the selected trunk is rendered busy to other selecting units. Relay'308 also closes a circuit from ground through its contact andouter lefthand armature, conductor 343, front contact and inner left-hand armature of relay 432, winding of relay'435, to battery and ground.

Relay 435 completes a circuit from ground through its middle lower armature and contact, conductor 436, rightJhan-d armature and contact of relay 431, contact '437, winding of relay 433 to battery and'ground. Relay 433 attracts .itsvarmature and closes a holding circuit for itself from battery, through its winding, contact 437, inner lefthand armature of said relay to ground at the contact and outer vleft-hand armature of `relay 409. Relay 433 also completes a circuit from battery, through the upper winding of relay 428, contact and innermost right-hand armature of relay 433, conductor 345, brush 303, and its normal position terminal, conductor 346, brush 203, terminal 213, conductor 214, through the windings of relay 114 to ground. Relay 114 attracts its armatures but due to its left-hand high resistance winding the marginal relay 428 is not able to energize.

The manipulation of they operators keyboard 515 for the purpose of registering the called line designation on the selected sending mechanism, will be considered before proceeding to describe the operation in volved in indicating the designa-tion of the selected idle trunk. Afterv the operator has received the officev and numerical designation from the calling subscriber and has actuated the proper oiiice key 500, she then proceeds, after an interval, to set up the desired number by 'depressing in succession the proper keys on her keyboard 515. As fully explained i`n` the Aabove mentioned British PatentNo. 173,00),-accepted December 12, 1921, the depression of these keys causes the designation to be recorded on the relay registers of the sendingmechanism which later servesl to control the selecting voperation of the switches 121 and 122 in the distant mechanical office to extend the connection to the called subscribers line.- Should the operatorl attempt to set up the designation on 'her keyboard prior to the time that the operators position switch 400 had found her position, or should all of the link circuits individual to the o'lice 120 be engaged, a signal to that effect is given the operator. When any of the keys on her keyboard 515l is depressed under these circumstances, a circuit iscompleted from battery, throughthe winding of relay 523, front contact and right-hand armature of relay 504, contact and outer right-hand armature of "relay 508, conductor 524, to ground either through resistance 525 vor 526 or one of the windings of relay 527 dependent upon the particular' y key operated.l Relay 523 completes a circuit for the illumination of lamp 530 which informs the operator that a link circuit has not yet been assigned to her for use.

If all of the sending mechanisms are found busy by the selecting switch 420, and consequently no sending mechanism is assigned to the calling operator, she is advised of this fact as soon as she depresses one of the keys on her keyboard 515. By the depression of any of the keys on keyboard 515, a circuit is closed, in this case, from battery, through the winding of relay 531, back contact and right-hand armature of relay 504, contact and outer 4right-hand armature of relay 508 to ground through resistance 525, resistance 526, or either of the windings of relay 527 according to the key operated. This circuitA leads through the back contact and armature of relay 504, which relayl it will be remembered becomes decnergized as soon :1s the operators position switch finds lthe calling position. Relay 531 attracts its armature and completes a circuit from the tone coil 533, contact and right-hand armature of relay 531, conductor 532 and thence to ground through the tertiary winding of the operators telephone set 118 shown in Fig. 1. This tone advises the operator that all the sending` mechanisms are busy.

l/Vheu an idle switching unit is allotted l'or use by the calling operatorvand the selecting `switch 420 finds an idle sending mechanism,

relay 434 in Fig. 4, energizes in the manner already explained. Relay 434 completes a circuit from ground., through the right-hand armature and contact of relay 502, winding CSL of relay 507, back contact and armature of relay 508, conductor 534, brush 404, inner upper armature and contact of relay) 43.4,.

conductor 438, brush 423 vand thence tobattery at the selected` sendingmechanism.- as

disclosed in theabove mentionedBritish Patent No. 173,009, accepted. D ecemben- 12,

1921'. Relay 507 becomes energized in this circuit and closes a circuit for itself.` from battery, through its armature and. contacts and :winding to ground at the. contact and right-hand armature of relay 502.

Relay `507 also completes afcircuit from battery, through its armature and contact; and winding ot' relay 508 to ground. Relay 503-be comes energizedl whereby \the. following actuation cfa key on the operator-7s keyboard is ineffective to cause the illumination of lamp 530 `or to produce a tone. in the 'operators receiver. The operators ykeyboard is now connected over conductors 524, 534, 535 andk 536, brushes 404, .405, andi406,,the Corresponding armatures and frontcontactso'i' relay 434, conductors 438,- 439 and,l `4,40, brushes423, 424 and 425 o'liswitch420f and thence vto the selected. sen/ding. mechanism.

`.'l`lie operator may thereupon proceed ,to reg- 121 and 122 are: positioned under-the control oi' the sending mechanism in accordance 1with. the'called line designation registered thereon. i c i f ai. consideration Will nextbefgiven ol.E the mechanism employedfor Visually indicating to the operator-the designation ofthe automatically selected trunlrinuorder thatshe may knowv which oneof tlleientir'e groupof trunks to use in extendingthe connection. For this purpose t-wol step-by-step.-switches 350 and 360,' the brushes of which-are respectively rdesignated 314 and 315 inFig. v3, .are provided. Eachiof the tente-rminals cooperating with brush 3 14i s connected, as shown, to the corresponding terminal in the iirst ygroup ofxten terminals of the side switch bank cooperatingwith brush 326 andalso to the corresponding-terminal 1n the second group ot ten terminals in said bank. In

' other words, terminal No. 0 of' switch 350 is connectedto terminal No. y0 in b oth the first and second groups of ten terminalsgin the side 'switch bank.' Terminal No.11fof switch 350 is connected.tozterminal-.No 1,01 boththe iirst and. second groupsiin the. teriminal bank` ,of the sidek switch, and `soi 0n. Each .of ithe teni terminals of fthe secondl step,-

pingy switch 360., with'zwfhich the brush315 .v

cooperates is connected to the correspondingly numbered terminals in; botlrtheuiirst and second group o1 ten'terminalsinonejot the banks oi'y each of the eight `trunk selecting switches. 'lliefmultiple connectinsbetween the terminals-of switch360 andthe terminalsofthe Abanks cooperating with brushes 306k and 206 of the first twoftrunk 'selectinot switches are shown.y in the drawing. The same method*f oi multiplmg thesel connections is employed, throughout( the entire series oi trunk selectingfswitches.-\y

It willibe recalled thatl the relay 308 was energized in response to theselection" of.4 an

idle trunk by; the trunkselecting..switch-200.iV

The relay 308 inaddition to v'completing1,the circ-uitv for relay 435` andrenderingl theselected= trunk busy-"as above' explainedgzcloses a circuit-` 'from battery, ,througlitheywinding of relay- 309,contact%A and right-hand arma ture olii-clay 308, conductor 363, tog-round at the outer. leftehand armature andfcontact of relay Helayg309r becomes-'energized and closes a cir/cuit from ground, throughits outer left-hand armature and contact, f con-ij tact and armature ofi relaylv 310,'y contactliand armature andy winding of steppng'magnet 312, .interrupter 332v to` battery and ground. Relay 309 'further completes a .circuit from grou-nd, ythrough itsl inner :left-handvarmature and contact,.contactandarmaturefof rela-y-I 311, contact and armature and :winding of stepping magnet 313, and1interrupter333 to battery and ground. The" stepping: magnet 312 which operates the stepping VvsW'itcli 350 is. energized and .-deenergized in response to 'theirst 4closurefand openingof theinterru'pter 332 'andf'advances `the .brush 314:1'- into engagement withdts first: or N 0.1 0. terminal. In thiswmancner, the brush-314 is `advanced from one terminal to the vnext until itreaches the thirdfforfNo. 2 terminal 352'. Inl-this'positioni, ya circuit is immediately. closed 1 ,from

battery through .the inner. right-hand armature andv contact ofy relay:l 309,'. windingf ot' relay 310., brush 314, terminalf352, terminal 353,v o n'which the'side switch briislif326 is standing; brush 326, brush-'.325'` and itsfthird positionwtermi-nal to ground'. Rla'y310 energizes andop'ens they operatingl circuit ot magnet 312 whereby the brush 314 ceases :to advance. For each energizationoffstepping magnet1312 as the brush 314 is steppingv orwar-d in search ot' a igrounded .terminal which represents .the numerical designation of'` the group* `of. trunks containingi the selected trunk, .a circuit is'completedffrom ground, y

through'the right-hand armature and contact ofmagnet 312,conductor 354, contact and Lupper armature oit relay-435pbrush 402,

conductor 537, winding of stepping magnet 511 to battery and ground. In response to the repeated closure of this circuit, magnet 511 steps the brush 510 to its third position terminal 538. f

Simultaneously with the operation of magnet 312, the stepping magnet 313 of switch 300 is also operated by the interrupter 333 and advances the brush' 315 over its successive terminals in search ot a grounded terminal. T he brush 315 continues to move until it reaches its No. 9 terminal 355. A circuit is then closed trom battery, through the outer right-hand armature and contact ot relay 309, winding ot relay 311, brush 315, terminal 355, multiple conductor 356, terminal 212, and brush 206 oif switch 200 to ground. Relay 311 energizes and opens the operating circuit of magnet 313, causing the brush 315 to discontinue its forward movement. For each operation of the stepping magnet 313 as the brush 315 steps torward to its No. 9 terminal 355, which corresponds to the units location ot the selected trunk in the third group ot ten trunks, a circuit is closed from ground, through the lett-hand` armature and contact of relay 313, conductor 358, contact and innermost lower armature of relay 435, brush 403, conductor 539, winding ot stepping magnet 521 to battery and ground. ln response to the closure ot' thisI circuit, stepping magnet 521 operates and advances the brush 520 through ten steps into engagement with its No. 9 terminal 540. On the first energization ot the stepping magnet 521, a circuit is closed trom battery, through the winding of relay 509. to `ground at the contact and lett-hand armature of magnet 521. Relay 509 energizes and closes a holding circuit for itself traceable 'trom battery, through the winding and Contact and inner right-hand armature ot said relay., conductor 541, to ground at the innermost lett-hand armature and contact el relay 502.

The relay 509 completes the circuits tor illumination ot the proper hundreds, tens and units lamps which indicate to the operator the designation ot the selected trunk outgoing to the mechanical ot'lice 120. The circuit tor the hundreds lamp 542 may be traced .trom battery, through said lamp, back contact and outer right-hand armature of relay 513, contact and inner left-hand armature ot relay 509 to ground. The circuit ot the llo. 2- tens lamp leads Yfrom loattery. through said lamp, terminal 538, brush 510, Contact and outer lett-hand armature of relay 509 to ground. The circuit of the No. 9 units lamp 544 leads from battery, tlirougggh said lamp, terminal 540, brush 520, to ground at the outer right-hand armature and contact of relay 509.

The operator, observing the illumination ot the indicator lamps, seizes the plug 110 ot her cord circuit and inserts it in vthe jack 111 ot the outgoing trunk, the number oic which is 029. A circuit is thereupon established from battery, through the lamp 123, resistance 124, sleeve of plug 110, sleeve of jack 111, winding of relay 112 to ground. Lamp 123 is illuminated and relay 112 becomes energized. Relay 112 completes a circuit from battery, through the winding of relay 113, contact and armature of relay 112, conductor 217, terminal 218, brush 202, conductor 211, brush 322, inner left-hand armature and front contact of relay 308 to ground. Relay 113 becomes energized and closes a holding circuit for itself as follows: battery, through the winding'ot said rela-y, contact and armature of relay 112, to ground at the closed contacts at the right-hand armature of relay 1.13.A At its right-hand armature and. contact the relay 113 also shunts the high resistance winding oi relay 114 from the circuit hereinloet'ore traced includ- I ing the upper winding ot marginal relay 428. Suiiicient current now flows in this circuit to permit the energization ot the marginal relay 428 which operates to initiate the release ot the equipment at the operators position. Relay 428 at its upper armature and contact opens the holding circuit of relay 408 which in turn releases its armatures. The retraction of the lett-hand armature of relay 408 opens the series holding circuit o'l relays 419, 501 and 502. At its righthand armature, relay 502 opens the holding circuits ot relays 505, 506 and 507. Relay 507 then causes the deenergization of relay At its innermost lett-hand armature, relay 502 opens the locking circuit ot relay 509. Relay 502 also closes a circuit, from battery, through the winding and Contact and armature ot stepping magnet 521, oli'- normal contact 522, which is closed during the time brush 520 is out of its normal position,v to ground at the contact and middle lett-hand armature otrelay 502. Magnet 521 interrupts its own circuit 'and restores the brush 520 to its normal position. Relay 502 also completes a circuit from battery, through the winding and armature and contact ot magnet 511, outermostv left-hand armature and Contact of relay 502, off normal contact 512, which is closed during the time brush 510 is out ot its normal position, to ground. Magnet 511 operates to step `the brush 510 back to its normal position. The

'apparatus at the operators positionis thus restored, ready to be taken for yuse in connection with subsequent calls.

'The relay 419 ot the switching unit, which also releases at the time relay 408 is deenergized, `opens the holding circuit of relay 432. Relay 432 becomes deenergized and opens the circuits of relays 435 and 434.

Relay 408 at its outermost right-hand armature and. back Contact closes a circuit l stored, remain in their normal positions since the operatingL circuits of magnets 312 and 313 are now opened at the armatures of relays 309, which relay was de-energizedby the retracL tionof the outer left-hand arma-ture'of relay 432. As soon ,as relays408 and 409 becomey deenergized the selecting unit shown in the drawing may be allotted by the allotter 410 forfurther use. It may happen that theselecting unit disclosed `is immediately allotted for use in connection with another call while switches 350 and 360 are returning to their normal positions. This jill make it possible for the selecting unit to be seized byanotlier opera-tor before the switches 350 and 360 havefully restored, in which case the return of these switches might interfere with thel transmission of the correct number of impulses toy select the ldesignation lamps at the second operators position. It will be noted that the relay 419 deenergized 7 uponthedeenergization of relay 408 and in so doing removes ground from the brush 401 which has been maintaining the operators position non-selectable by other operators position switches. Should another operator seize theselecting unit shown and should the ground be removed from the brush 401, the operators position switch 400 would immediately operate toind the second operators position, all of which might occur before the switches 350 and 360 had restored. Therefore, to guard against this condition the operators switch 400 is caused to actuate continually, provided the unit is appropriated by another operator, and not to seize that operators position until the switches 350 and 360-are in condition to perform their haveffound an Aidle trunk. The operators position switch 400 is functions when the trunk'selectingv s witches v caused to rotate continually by means of holding a ground potential on the test brush 401 Aafter the relay 408 becomes. deenergized.

- This potential may be applied from ground either at the off-normal contact 318 oi' the off-normal contact 319 of the switches 350 and 360, respectively, conductor 359, thence to `the brush 401. lf at this time the coil 415 has' been-'unbalanced and relay 417 operated, the circuit previously. traced for magnet407 isv established andv leads through the outer left contact of relay 417, left baci: contact of relay 418 to the grounded con:` ductor 359. This ground is maintained on the conductor 359 vtol cause the continued operation .of magnet 407 until both switches 350 and 360 have restored, whereby the offnoiinal contacts 318 and 319 are both opened. After the contacts 318 and 319 opened `the switch 400continuesto rotateuntil it position in the manner iinds the operators previously explainec.

As soon as the sending mechanism has completed its function of 'controlling the selecting operation of the switches 121 and 122, the battery potential, which, up to this Lil time, has been maintaining the energizati'on of relay 431 over the circuit including brush 426, is removed in the manner explained in the above mentioned British Patent No.y

173,009, accepted December 12, 1921. Relay 431 becomes deenergized and opens the substitute locking circuit of relay 409. Relay 409 becomes deenei'gized since, as will be re-` called, tlie original locking'circuit therefor is openedat this time bythe lower armature `and contact of the marginal relay 428. Relay 409 on deenergizing, opens the series circuit through the winding of the stepping magnet 207 and relay 308. Relay 3.08 at its inner left-hand armature opens the original the circuit which, upto thisv time, has been maintaining the energization of the inargin nal relay 428 in series with the low resistance il Vwinding of relay 114. Relays 428r and 114 therefore become deenergized. Relay 114 disconnects thetrunk conductors 13.1 and 132 from the switch controlling conductors 215 and 216 and extends them-to the righthand windings of the repeating coil 109 in the operators cord circuit.

lWhen the called subscriber answers, the supervisory relay 108 in the operators cord circuit is energized in the usual manner and completes a circuit from battery, through the contact and armature of said relay, rcf sistance` 133 .resistance 124 to ground through the winding of relay 112. This circuit shunts out thelamp 123 thus informing` 4the operator that .the called subscriber has answered. 1

At the termination of the conversation, the calling and called subscribers, by replacing their receivers on the switch hooks,

ico

vLerares? cause the deencrgization of relays 107 and 103 1.rhicln in' turn, permit the illumination of the supervisory lamps 106 and 123. The operator then removes the plugs of her cord circuit from the jack 101 of the calling line, and jack 111 o'f the outgoing trunkvcircuit and relays 105 and 112 become deenergized. Relay 112, in. turn, causes the deenergization ot relay 113.

Should the sending mechanism complete its function ot controlling the switches in the distant. mechanical olice prior to the time the operator inserts the plug 110 in jack 111 ot the outgoing trunk, the relay 431 would become deenergized, as explained, in advance ot the deenergization of relay 428. The deenergization oi relay 431, in this case, is vWithout eliect, since the relay 409 depends for its release jointly upon the release of relay 431 and the energization of relay 428. its soon thereafter, as the operator inserts the plug in the ack, the relay 423 becomes deenergized as described, to in turn cause the release oli relay 409`Which brings about the results already explained. It will next be assumed that all the trunks in the lirst hundred are busy when the trunk selecting switches perform their hunting operation. lt Will also be assumed that the first idle trunk to be found in the second hundred is trunk No. 129. rlhe trunk selecting switches, therefore, operate in succession, one after another and the side switch 320 moves forward onefstep for each group of ten trunks hunted over. Since the selected idle trunk now re ides in the first ten trunks of the seventh group o'j twenty, the side switch brush 326 is standing on its No. 2 position terminal 361 in the second halt of the bank and brush 325 is standingon un open terminal.' The units designation ot' the trunk being the saine as in the case previously assumed the brush corresponding to brush 206 of the particular' trunk selecting switch taken for use is in engagement with its No. 9 position terminal in the first halt of the bank. When the side svsitch is standing in any one of its first ten positions, the olli-normal contact 329 controlled thereby,`is closed. A circuit is therefore completed from battery through the Winding ot relay 331, right-hand larn'iature and Contact of relay 330, contact 329, conductor 362 to Iground at the Contact and middle lett-hand armature ot relay 409. ll'elay 331attracts its armature and closes a circuit for itself in series with relay 330 to ground as just described. llelay 330 does not energize, however, since its Winding is shunted out by the direct circuit closed through the oit-normal contact W hen the side switch brush 326 leaves the last position in the irst half of its bank, the contact 329is opened and. relay ener- EEE gizes in series with relay 331. From here on, the operation of the system is the same as described, up to the point Where relay 309 is energized and the switch 350 conrmences to operate under the control of its stepping magnet 312. Since the brush 326 is standing on terminal 361 in the second haltn ot the bank, the brush 314 is driven through al complete cycle Without funding a grounded terminal. Consequently the vbrush 510, which operates in synchronism with brush 314, makes a complete movement over its terminal bank. llllhen brush 510 first leaves its normal position, contact 512 is closed and a circuit is established from battery, through the Winding of relay 514, inner armatureand contact of relay 513 to ground at the contact 512. Relay 514 attracts its armature and completes a circuit for itself in series with relay 513 to ground at the contact and innermost left-hand armature of relay 502. Relay 513 does not energize, however, since its Winding is shunted out by the direct circuit closed to ground at off-norn'lal contact 512. As soon as the brush 510 has taken ten steps and returns to its normal position, contact 512 is opened and relay 513 is energized in series ivith relay 514. The brush 314v ol: switch 350 continues to move through a second cycle. -On reaching its No. 2 terminal 352, a circuit is completed from ground, through the contact and left-hand armature of relay 330, brush 326, terminal 361, terminal 352,v brush 314, Winding of relay 310, and inner right-hand armature and contact of relay 309 to battery and ground. Relay 310 energizes and causes the switch 350 to cease its rotation as hereinbefore described.

llllhen the selection ot the. units lamp has been completed and relay 509 is energized,

a circuit tor the No. 1 hundreds lamp'51l5 is completed as .tollows:battery,through the lamp 545, 'front contact and outer armature ot relay 513, to ground at the contact and inner left-hand armature ot relay 509. The operator, olfiserviug the illumination oi? lamp 545 knows that trunk No. 29 in the No. 1 hundred has been selected for use.

llVhat is claimed is:

1. In a telephone exchange system, an operator-ls position, a plurality of trunks ar rance l in groups at said position, trunk selee ing devices, one for each group, means for operating said selecting devices to select a trunk in any of said groups, indicator selecting means,means controlled in accordance with which one of said trunk selecting devices is taken for use for determining the extent ot operation ol said indicator selecting means, indicator devices, and means controlled by said indicator selecting means for imi-iably operating said indicator devices to indicate the gro-up of trunks containing the selected trunk and the location of the selected trunk in such group.l i

2. ln a telephone exchange system, an operatoi"s position, a plurality of trunks arranged in groups at said position, means at tliegoperatons position for extending telephone connections over said trunks, trunk selecting switches, oneA for each group ot trunks, means for operating` said switches to select a trunk in any of said groups, indicator devices for indicating the group containing the selected trunk and the location of such trunk in the group, indicator selecting means or selecting said indicator devices, and means dependent on which trunk selecting switch is taken vfor use for determining the extent of operation of said in dicator selecting means.

8; In a telephone exchange system, an operators position, a plurality of trunks ain ranged in groups at said position, means conytrolled by the operator for extending telephone connections over said trunks,`trunk selecting switches, one tor each group ot trunks, means for operating said switches to automatically select a trunk in' any ot said groups, indicatorvdevices'for indicating to the operator the designation ofthe group containing` the selected trunk and the desi nation of the selected trunk in such group,

variably operable indica-tor selecting means for selecting said indicator' devices, and means dependent on which one oit said trunk selecting switches is taken for use for determining the extent of operation of said indicator selecting means;

i ll. In a telephone exchange system, an operatoi"s' position, a plurality of trunks arranged in groups at said position, means controlled bythe operator for extending tele-r phone connections over said trunks, trunk selecting switches, one for each group ot trunks, means for operating` said switches to i' automatically select atrunk in any of said groupsindicator-devices for indicating to the' operator the designation of the group containing the selected trunk and the designation of the selected trunk in such group, variably operable indicator selecting` means for selecting said indicator devices,` andv means dependent on which one of said trunk 'selectingswitches is taken toruse, and on theoperation ot suoli switch,` for deterr mining the extent of operation of said indidetermining the extent ot operation of said Aindicas-tor means,

6, In a telephone exchange system, an operators position, a plurality yoi trunks arranged iii groupsat said position, means at said-position for extending telephone connections over said trunks, trunk selecting switches, one for each group ot trunks, meansy `for operating said switches rin. succession to automatically select an idletrunk,

indicator devices for indicating lthe designa ion of the group containing the selected trunk and the designation of` the selected trunk in the group, variablyoperable indicator selecting means for selecting said indi,- cator devices, and means dependenton which one ot said trunk selecting switches is taken for use for determining the' extentof operation of said indicator selecting means.

7. In a telephone exchange system, an operators position, a plurality of'trunksarranged in groups at said position, means at said posit-ion for extending telephone con-i.`

nections over said trunks, a series trunk switches one" foi each group` of` trunks,

means 'for operating vsaid switches in suc-.

cession to `automatically select a .group containing an idle trunkand to select `the idle trunk in suchgroup, indicator devices for indicating the designation of the selected group and the designation of theselected eol - leo ceeding switchesto automatically select a groupv containing an idle trunk andr to select an idle trunkV in such group, indiof the selected group andf the designation of the selected trunk in the'group, variably operable indicator selecting means f for selecting said devices, and means dependent `on rwhich one `ot saidy trunk selecting switches'is takenifor use vand-on the op'- eration .oit such switch for determining the Acatordevices for .indicating the designation extent of operation ot said indicator selecting means.

9. ln a telephone exchange system, tele phone lines, an operators position, a plurality of trunks arranged in groups at said position, means for connecting the telephone lines to said trunks, automatic switches for extending said trunks, trunk switches, one ior each group ot trunks, means tor operating said trunk switches to select an idle trunk, indicator devices for indicating the group containing the selected trunk and the location of the trunk in such group, variably operable indicator selecting means for selecting` said indicator devices, means dependent on which trunk switch is taken ior use tor determining the extent ot' operation of said indicator selecting means, and means controlled by lthe operator for controlling the operation of said automatic switches.

10. In a telephone exchange system, telephone lines, an operators position, a plurality of trunks arranged groups at said position, means Jiior connecting the telephone lines to said jtrunks, 'automatic switches for extending said trunks, trunk switches, one for each group ot trunks, means for operating said trunk switches to select an idle trunk, indicator devices for indicating the group containing` the selected trunk and the location of the trunk in such group, variably operable indicator selecting means for selecting said indicator devices, means dependent on which trunk switch is taken for use for determining the extent of operation oi said indicator selecting means, and means controlled by the operator 'for controlling the operation of said automatic switches over the selected trunk.

l1. n a telephone exchange system, an

operators position, a plurality ot trunks arranged in groups at said position, trunk switches, one for each group of trunks, means for operating said switches to select an idle trunk, indicator devices for indicating the designation of the group containing the selected trunk, a variably operable indicator selecting switch for selecting said devices, and means dependent on which one ot said trunk switches is taken for use for determining the extent of operation of said indicator selecting switch.

l2. in a telephone exchange system, an operators position, a plurality or" trunks arranged in groups at said position, trunk switches, one for each group of trunks, means for operating saidswitches to select an idle trunk, indicator lamps for indicating the designation of the group containing the selected trunk, a variably operable stepby-step switch for selecting' said lamps, and means dependent on which one oi said trunk switches is taken for use tor determining the operation of said step-by-step switch.

13. In a telephone exchange system, an operators position, a plurality of trunks arranged in groups at said position, trunk switches, one ior each group of trunks, means for operating said switches tol select an idle trunk, an auxiliary switch for controlling the operation orp said trunk switches, means i''or positioning the auxiliary switch in accordance with which one of said trunk switches is taken for use, indicator devices for indicating the designation of the selected trunk, a variably operable indicator selecting switch for selecting said devices,

and means dependent. upon the position taken by said auxiliary switch for determining the operation of said indicator selecting switch. i

14;. n a telephone exchange system, an operators position, a plurality of trunks arranged in groups at said position, trunk switches, one for each group of trunks,

means for operating` said switches to select an idle trunk, indicator devices for indicatino" the designation of the trunk groups, an indicator selecting switch for selecting said devices, means dependent on which one oi said trunk switches is engaged for use 'for determining the operation of said selooting switch, other indicator devices for indicating the designation or" the trunks in a group, a second selecting switch for selecting said last named devices, and means dependent on the operation of the trunk switch engaged for use for determining the operation ot said second selecting switch.

ln witness whereof, I hereunto subscribe my name this 12th day of May, A. D. 1920.

EDGAR H. CLARK. 

